Comparison of pregnancy rates following frozen embryo transfer according to the reason for freezing: risk of ovarian hyperstimulation vs inadequate endometrial thickness

Purpose: To determine the relative pregnancy rates following frozen embryo transfer according to the reason for deferring fresh embryo transfer and freezing all embryos. Method: A retrospective review over a 10-year time period of all in vitro fertilization (IVF) cycles that deferred fresh transfer and cryopreserved all embryos related to risk of ovarian hyperstimulation syndrome or if there was inadequate endometrial thickness. Pregnancy rates according to the reason for freezing were then compared. Results: The clinical and live delivered pregnancy rates following frozen embryo transfer in women <= age 39 was 42.8% and 31.9%, respectively for women deferring for risk of ovarian hyperstimulation syndrome vs 28.7% and 21.8% for those freezing for inadequate endometrial thickness (p = 0.01 and p = 0.07, respectively). Conclusion: Embryo cryopreservation may not be a complete panacea for problems of inadequate endometrial thickness.